1. Field of the Invention
The present invention relates to a method and system for indicating system characteristics of one processing system to another processing system.
2. Description of the Related Art
FIG. 1 illustrates a hardware environment of a channel subsystem 2 included in a host system 4 providing communication between CPUs 6a, b and I/O devices 10a, b, c. A storage controller 8 controls access to the I/O devices 10a, b, c. The host system 4 communicates with the storage controller 8 via the channel subsystem 2 and subchannels 14a, b, c therein. The host system 4 includes CPUs 6a, b that contain the sequencing and processing facilities for instruction execution, interruption action, timing functions, initial program loading, and other machine-related functions. The I/O devices 10a, b, c may be comprised of printers, magnetic-tape units, direct-access-storage devices (DASDs), displays, keyboards, communications controllers, teleprocessing devices, and sensor-based equipment. The storage controller 8 regulates and controls data transfers to the I/O devices 10a, b, c. The storage controller 8 function may be a separate stand alone machine, such as the IBM 3990 Storage Controller, or housed within the I/O device 10a, b, c or within the host system 4. In certain systems, the host system 4 may view the storage controller 8 as a multitude of separate control unit images or logical subsystems (LSSs), wherein each control unit image provides access to one or more I/O devices 10a, b, c. The storage controller 8 may include multiple control unit images, i.e., LSSs, each of which may address up to 256 I/O devices.
The CPUs 6a, b and the channel subsystem 2 may access a main storage 12. Programs and data maintained in the I/O devices 10a, b, c such as storage drives, must be loaded into the main storage 12 before the CPUs 6a, b can process such programs and data. The main storage 12 may include a fast access buffer or cache. I/O operations involve the transfer of data between the main storage 12 and the I/O devices 10a, b, c. The channel subsystem 2 directs the flow of data between the storage controller 8 and the main storage 12. The channel subsystem 2 relieves the CPUs 6a, b of handling I/O operations and permits the CPUs 6a, b to devote processing cycles to other operations while the channel subsystem 2 concurrently handles data transfers. In typical implementations, the CPUs 6a, b, the main storage 12, and the channel subsystem 2 are all located within a single host 4 that is attached to a single storage controller 8, such as the IBM 3990 Storage Controller.
Channel paths 13 provide data communication between the channel subsystem 2 and the storage controller 8. The channel paths 13 may employ a parallel-transmission protocol or a serial-transmission protocol. The storage controller 8 includes control logic to physically access the I/O devices 10a, b, c and control data transfer. In preferred embodiments, multiple channel paths 13 may be dedicated for communication with a particular I/O device 10a, b, c.
A subchannel 14a, b, c is dedicated to each I/O device 10a, b, c accessible to the channel subsystem 2, i.e., there is a one-to-one relationship between subchannels 14a, b, c and I/O devices 10a, b, c. Each subchannel 14a, b, c consists of internal storage and includes information relating the I/O devices 10a, b, c to the channel subsystem 2. The channel subsystem 2 uses the information in the subchannels 14a, b, c to access the I/O devices 10a, b, c. The subchannels 14a, b, c are assigned to the I/O devices 10a, b, c at initialization. The subchannels 14a, b, c maintain information such as the channel command word (CCW), channel-path identifier, device number, etc., concerning operations initiated with respect to the I/O device 10a, b, c represented by the subchannel 14a, b, c. I/O devices 10a, b, c that are attached to the channel subsystem 2 by multiple channel paths 13 may be accessed using any of the available channel paths 13. An I/O device 10a, b, c is addressed by channel-path identifiers (CHPIDs) identifying the path to a device, subchannel numbers identifying the subchannel 14a, b, c associated with the device, and a device number uniquely identifying the I/O device 10a, b, c to the host system 4. The IBM S/390 operating system allows for dynamic-reconnection, wherein the storage controller 8 may select any channel path 13 leading to the host system 4 when logically reconnecting to the channel subsystem 2. A description of these commands is provided in the IBM publication, "IBM 3990/9390 Storage Control Reference," IBM Document no. GA32-0274-04 (Copyright IBM, 1994, 1996), which publication is incorporated herein by reference in its entirety.
In the IBM mainframe environment, the channel paths 13 from a host system 4 to the storage controller 8 are identified to the storage controller 8 by a Set Path Group Identifier command. This command assigns a path group ID to one or more channel paths that provide communication between a host system 4 and one of the I/O devices 10a, b, c. Thus, a subchannel 14a, b, c is related to a path group ID, which relates the paths to an I/O device 10a, b, c associated with the subchannel 14a, b, c. The path group IDs define the paths associated with a host 4 for the purpose of device reservation.
In prior art systems, it is possible for a host 4 to concurrently run two or more operating systems--a host operating system and a guest operating system which runs on top of the host operating For instance, the IBM VM/ESA.RTM. operating system supports running a guest system with a different operating system date/time than the host VM/ESA system. This enables testing of MVS.RTM., VM, and VSE/ESA.TM. systems with different application programs without affecting the host VM/ESA system. VM/ESA and MVS are registered trademarks of IBM and VM/ESA is a trademark of IBM. However, one problem that may arise in such a system is that the guest operating system may have enhanced function capability beyond the capabilities of the host operating system. In such case, the host operating system would not be able to understand certain commands and operations from the storage controller 8 when the storage controller 8 is interacting with the guest operating system in the enhanced capability modes.
In prior art systems, the host may issue commands to inhibit the enhanced operations. For instance, in the IBM mainframe environment, the host system 4 may issue a Set Special Intercept Condition which causes the host operating system to monitor communications from the storage controller 8 to the guest operating system. Under control of the Set Special Intercept Condition, the host 4 monitors commands on a path group. The host operating system may then intercept certain specified commands from the storage controller 8 to the guest operating system on a path associated with the path group ID being monitored and prevent such commands from reaching the guest operating systems. These commands and intercept methods are described in IBM publication "Storage Subsystem Library: IBM 3990 Storage Control Reference (Models 1, 2, and 3)", IBM document no. GA32-0099-06, (IBM Copyright 1988, 1994), which publication is incorporated herein by reference in its entirety.
Alternatively, to prevent a storage controller 8 implementing operations incompatible with the host system 4 capabilities, a systems administrator may selectively disable certain functions in the storage controller 8 that the host operating system cannot handle.
There is a need in the art for an improved method and system of determining and enabling system capabilities.